This prospective, double blind, placebo-controlled, parallel group study will be conducted in three study centers in Guangzhou, China. Patients aged older than 65 (ASA I-III) undergoing primary elective abdominal surgery with general anesthesia will be involved in this study. According to previous studies and our pilot trial, the sample size was estimated to be 900 subjects (each center recruiting 300 patients). All eligible patients will be randomly assigned to one of two groups: study group receiving parecoxib and control group receiving normal saline. All patients will be managed with by a standard clinical anesthesia protocol with a sevoflurane-based general anesthesia with continuous intravenous remifentanil, followed by a postoperative PCA with morphine. The emergence delirium will be evaluated by two persons blinding to medication and grouping using Riker sedation-agitation scale immediately since tracheal extubation and at specific time points until patients being discharged from PACU. Pain intensity assessments and pain relief assessments will also be conducted by the patients at given time points in 2 days postoperatively. The morphine-sparing effect, tolerability and safety of parecoxib will be investigated as well.